Lithium Rechargeable Battery

ABSTRACT

Lithium rechargeable batteries having functional center pins are provided. A lithium rechargeable battery has a center pin whose top and bottom ends are blocked by a thermal cut-off composition to reduce the void volume inside a bare cell during initial overcharge. The thermal cut-off composition melts at a temperature within a specific temperature range, e.g. between about 80 and about 250° C. This prevents the battery from exploding and igniting. Thus, the inventive lithium rechargeable batteries have improved thermal stability.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 11/414,744, filed Apr. 27, 2006 which claims priority to andthe benefit of Korean Patent Application No. 10-2005-0037286, filed onMay 3, 2005, in the Korean Intellectual Property Office, the entirecontent of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a lithium rechargeable battery having afunctional center pin. More particularly, the present invention relatesto a lithium rechargeable battery having a center pin whose top end andbottom end are blocked with a thermal cut off composition so as toreduce the void volume inside the bare cell at initial overcharge. Thethermal cut off composition is molten at temperatures ranging from about80 to about 250° C. to prevent the battery from exploding and igniting,and to improve the thermal stability of the battery.

BACKGROUND OF THE INVENTION

As generally known in the art, a cylindrical lithium rechargeablebattery includes a cylindrical electrode assembly having a center pin, acylindrical can to which the electrode assembly is coupled, and a capassembly coupled to the top opening of the can for sealing the can.

Such lithium rechargeable batteries generally have capacities rangingfrom 2000 to 2400 mA, and have been widely used for notebook PCs,digital cameras, camcorders, and the like, which require electric powerwith high capacity. Additionally, such rechargeable batteries areconnected in series or in parallel to provide a desired voltage orcapacity, and take the form of battery packs having predetermined shapesand including safety devices.

In one conventional cylindrical lithium rechargeable battery, an anodeplate coated with an anode active material, a separator, and a cathodeplate coated with a cathode active material are stacked and one end ofthe stacked structure is coupled to a bar-shaped winding axis. Thestructure is then wound into the shape of a cylinder to form anelectrode assembly. Next, a center pin is coupled to the electrodeassembly and the resultant structure is inserted into a cylindrical can.Then, an electrolyte is injected into the cylindrical can and a capassembly is coupled to the top of the cylindrical can to complete asubstantially cylindrical bare cell.

The cylindrical lithium secondary battery described above also includesa safety device for preventing the battery from exploding uponovercharge. The safety device includes a safety vent capable ofdeformation upon increases in the internal pressure of the battery dueto overcharge. The battery also includes a current interruption device(CID) that interrupts the circuit through the substrate which isdeformed due to the deformation of the safety vent. In addition, thebattery includes a secondary protection device that interrupts thecircuit upon increases in temperature.

Such safety devices operate as follows. When a lithium rechargeablebattery is in an overcharged state, the electrolyte in the batteryevaporates from the top region of the electrode assembly, therebyincreasing electric resistance. Additionally, the central portion of theelectrode assembly deforms, resulting in precipitation of lithium.Further, the battery undergoes a rapid increase in temperature becausethe increased electric resistance at the top region of the electrodeassembly causes local heat emission.

Under these circumstances, the internal pressure of the battery rapidlyincreases due to the additives in the electrolyte, such as cyclohexylbenzene (CHB) and biphenyl (BP). Such additives decompose uponovercharge and generate gas. The increased internal pressure pushes thesafety vent (which is part of the cap assembly) out of its place,causing the current interruption device (CID) disposed over the safetydevice to break, which results in interruption of the electric current.In other words, the printed circuit pattern formed on the CID is broken,thereby interrupting the electric current. Current interruption resultsin termination of the overcharged state, thereby making it possible toprevent the battery from exploding and igniting. Also, if the internalpressure of the battery is greater than the critical pressure due toovercharge, the safety vent may break, discharging gas to the exteriorof the bare cell through an opening in the upper cap plate.

The center pin may be made cylindrical in shape by winding a metalplate. Alternatively, the center pin may originally be formed into anintegral cylinder. When the center pin comprises a wound metal plate,the metal plate includes a slit where both ends of the metal platecontact each other. Thus, an electrolyte or gas may be transferredthrough the slit. When the center pin is an integral cylinder, there isa void volume inside the center pin. The void volume causes delay in thedeformation or breakage of the safety vent. The void volume must bereduced in initial overcharge to allow the safety vent to operatepromptly and to permit the center pin to serve as a gas discharge pathwhen the internal temperature of the battery reaches 80 to 250° C.

SUMMARY OF THE INVENTION

The present invention addresses the above-mentioned problems. In oneembodiment of the present invention, a lithium rechargeable battery hasimproved safety by including a center pin whose top and bottom ends areblocked with a thermal cut off composition to reduce the void volume ininitial overcharge. The thermal cutoff composition permits the safetyvent to operate promptly, and the thermal cut-off composition melts whenthe internal temperature of the battery reaches a predetermined value,thereby permitting the center pin to serve as a gas discharge port.

In one embodiment, such a lithium rechargeable battery includes anelectrode assembly having a center pin inserted in its center, a can forhousing the electrode assembly, and a cap assembly for sealing the can.The center pin is blocked at its top and bottom ends with a thermal cutoff composition. The surface of the thermal cut-off composition may becoated with any one of polyethylene (PE), polypropylene (PP), andpolyimide (PI).

According to one embodiment of the present invention, the thermalcut-off composition melts or explodes at a temperature ranging fromabout 50 to about 250° C. In another embodiment, the thermal cut-offcomposition melts or explodes at a temperature ranging from about 80 toabout 150° C. Therefore, in one embodiment, the thermal cut-offcomposition may include an organic compound having a melting pointranging from about 80 to about 150° C. Nonlimiting examples of suchorganic compounds include 4-hydroxy-3-methoxybenzaldehyde,1,3-diphenylbenzene, 1,4-dibromobenzene, triphenylmethane,4,4′-methylenebis(benzeneamine), diphenylethanedione, pentanedioic acid,n-propyl-4-hydroxybenzoate, xanthene, 3,5-dimethylpyrazole,1,3-benzenediol, N-phenyl-2-naphthylamine, N-phenylacetamide,9H-fluorene, m-phenylenedibenzoate, and dihydro-2,5-furanedione.

Additionally, the thermal cut-off composition may include a combinationof at least two organic compounds. Nonlimiting examples of organiccompounds for use in this embodiment include 2H-1-benzopyran-2-one,n-butylhydroxybenzoate, phenylbenzoate, diphenylphthalate,4-hydroxy-3-methoxybenzaldehyde, 1,3-diphenylbenzene,1,4-dibromobenzene, triphenylmethane, 4,4′-methylenebis(benzeneamine),diphenylethanedione, pentadioic acid, n-propylhydroxybenzoate, xanthene,3,5-dimethylpyrazole, 1,3-benzenediol, N-phenyl-2-naphthylamine,N-phenylacetamide, 9H-fluorene, m-phenylenedibenzoate,dihydro-2,5-furanedione, 2,5-pyrollidinedione, 3-pyridinecarboxamide,phthalic anhydride, p-toluene sulfonamide, dimethyl terephthalate,N-(4-methylphenyl)acetamide, hexanedioic acid, N-phenylbenzamide,4,4′-dibromobiphenyl, mannitol, 4-(1,1-dimethylethyl)benzoic acid,N-(2,6-dimethylphenyl)acetamide, 2,4-dinitrobenzeneamine,7-hydroxy-4-methylcoumarine,5,5-diethyl-2,4,6(1H,3H,5H)pyrimidinetrione, 1,4-diphenylbenzene,inocitol, 6-phenyl-1,3,5-pyrazine-2,4-diamine,3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione, 1,1′-bi-2-naphthol,4-hydroxy-3-methoxybenzoic acid, 2,3-dimethylanthraquinone,2-phenylindole, 2-methylphenylacetic acid, 2-phenylbenzimidazole,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,hydantoin, 7-hydroxycoumarine, carbanilide, 1,5-dichloroanthraquinone,1,1,1-tris(4-hydroxyphenyl)ethane, 1-aminoanthraquinone,2,3,5,6-tetrabromo-p-xylene, 1,5-dihydroxynaphthalene, 2-quinoxalinol,2,4-diamino-6-methyl-1,3,5-triazine, 7-chloro-4-hydroxyquinoline,alizarine, anthraquinone, 2,4-diamino-6-hydroxypyrimidine,2-phenylbenzimidazole, 2-amino-4-hydroxy-6-methylpyrimidine,4-amino-2,6-dihydroxypyrimidine, 2-amino-4,6-dihydroxypyrimidine anduracil. In one embodiment, the thermal cut-off composition isnon-conductive.

According to one embodiment of the present invention, the center pinincludes a body having a predetermined length which is open at its topand bottom ends. The center pin also includes a blocker including athermal cut-off composition, blocking the top and bottom ends of thebody. The thermal cutoff composition melts or explodes at apredetermined temperature. The body may be formed of any suitablematerial such as steel, stainless steel or aluminum. Also, the body mayhave tapered portions at its top and bottom ends. The blocker may be anenvelope shaped film that surrounds the body, including the top andbottom ends of the body. Alternatively, the blocker may be a lid thatblocks the top and bottom ends of the body. The body may further includea gasifier disposed inside the body which decomposes at a predeterminedvoltage range to generate gas. Nonlimiting examples of suitablematerials for the gasifier include cyclohexyl benzene (CHB) and biphenyl(BP). In addition, the body may further include a flame retardant, whichincludes at least one material selected from the group consisting ofmagnesium hydroxide-based materials, aluminum hydroxide-based materialsand phosphate-based materials.

In another embodiment of the present invention, a lithium rechargeablebattery includes an electrode assembly having a center pin inserted inits center, a can for housing the electrode assembly, and a cap assemblyfor sealing the can. The center pin includes a compressed compressionspring inserted into a thermal cut-off composition, a body surroundingthe compression spring, and lids for blocking the top and bottom ends ofthe body. The surface of thermal cut-off composition may be coated withany suitable material, such as polyethylene (PE), polypropylene (PP), orpolyimide (PI). The thermal cut-off composition melts or explodes at atemperature ranging from about 50 to about 250° C. In anotherembodiment, the thermal cut-off composition melts or explodes at atemperature ranging from about 80 to about 150° C. The thermal cut-offcomposition includes an organic compound. Nonlimiting examples ofsuitable organic compounds include 4-hydroxy-3-methoxybenzaldehyde,1,3-diphenylbenzene, 1,4-dibromobenzene, triphenylmethane,4,4′-methylenebis(benzeneamine), diphenylethanedione, pentanedioic acid,n-propyl-4-hydroxybenzoate, xanthene, 3,5-dimethylpyrazole,1,3-benzenediol, N-phenyl-2-naphthylamine, N-phenylacetamide,9H-fluorene, m-phenylenedibenzoate, and dihydro-2,5-furanedione.Alternatively, the thermal cut-off composition may include a combinationof at least two organic compounds. Nonlimiting examples of suitableorganic compounds for use in this embodiment include2H-1-benzopyran-2-one, n-butyl-4-hydroxybenzoate, phenylbenzoate,diphenylphthalate, 4-hydroxy-3-methoxybenzaldehyde, 1,3-diphenylbenzene,1,4-dibromobenzene, triphenylmethane, 4,4′-methylenebis(benzeneamine),diphenylethanedione, pentadioic acid, n-propyl-4-hydroxybenzoate,xanthene, 3,5-dimethylpyrazole, 1,3-benzenediol,N-phenyl-2-naphthylamine, N-phenylacetamide, 9H-fluorene,m-phenylenedibenzoate, dihydro-2,5-furanedione, 2,5-pyrollidinedione,3-pyridinecarboxamide, phthalic anhydride, p-toluene sulfonamide,dimethyl terephthalate, N-(4-methylphenyl)acetamide, hexanedioic acid,N-phenylbenzamide, 4,4′-dibromobiphenyl, mannitol,4-(1,1-dimethylethyl)benzoic acid, N-(2,6-dimethylphenyl)acetamide,2,4-dinitrobenzeneamine, 7-hydroxy-4-methylcoumarine,5,5-diethyl-2,4,6(1H,3H,5H)-pyrimidinetrione, 1,4-diphenylbenzene,inocitol, 6-phenyl-1,3,5-pyrazine-2,4-diamine,3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione, 1,1′-bi-2-naphthol,4-hydroxy-3-methoxybenzoic acid, 2,3-dimethylanthraquinone,2-phenylindole, 2-methylphenylacetic acid, 2-phenylbenzimidazole,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,hydantoin, 7-hydroxycoumarine, carbanilide, 1,5-dichloroanthraquinone,1,1,1-tris(4-hydroxyphenyl)ethane, 1-aminoanthraquinone,2,3,5,6-tetrabromo-p-xylene, 1,5-dihydroxynaphthalene, 2-quinoxalinol,2,4-diamino-6-methyl-1,3,5-triazine, 7-chloro-4-hydroxyquinoline,alizarine, anthraquinone, 2,4-diamino-6-hydroxypyrimidine,2-phenylbenzimidazole, 2-amino-4-hydroxy-6-methylpyrimidine,4-amino-2,6-dihydroxypyrimidine, 2-amino-4,6-dihydroxypyrimidine anduracil.

The lids have a degree of strength such that the lids are opened orbroken by the restoration force of the compression spring. The lids maybe formed of a polymer resin. The body may further include a gasifierdisposed inside the body which decomposes at a predetermined voltagerange to generate gas. Nonlimiting examples of suitable materials forthe gasifier include cyclohexyl benzene (CHB) and biphenyl (BP). Inaddition, the body may further include a flame retardant, which includesat least one material selected from the group consisting of magnesiumhydroxide-based materials, aluminum hydroxide-based materials andphosphate-based materials.

Insertion of the compression spring into the thermal cut-off compositionmay be accomplished by insert injection molding. Further, the surface ofthe thermal cut-off composition may be coated with any suitablematerial, such as polyethylene (PE), polypropylene (PP), or polyimide(PI).

The center pin may have indentations, each indentation being spacedapart from the top and bottom ends of the main body by a predetermineddistance. These indentations enable fixation of the blocker. In anotherembodiment, the center pin may include a body having a predeterminedlength and open top and bottom ends, lids for blocking the top andbottom ends of the body, and a sealing member between the lid and eachof the top and bottom ends to seal the body. The sealing member includesa thermal cut-off composition which melts or explodes at a predeterminedtemperature.

The lids may be formed of polymer resins. The thermal cut-offcomposition melts at a temperature ranging from about 50 to about 250°C. In another embodiment, the thermal cut-off composition melts at atemperature ranging from about 80 to about 150° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent with reference to the followingdetailed description when considered in conjunction with theaccompanying drawings, in which:

FIG. 1 is a perspective view of a lithium rechargeable battery accordingto one embodiment of the present invention;

FIG. 2 is a sectional view of the battery of FIG. 1, taken along line2-2;

FIG. 3 a is a perspective view of a center pin according to oneembodiment of the present invention;

FIG. 3 b is a sectional view of the center pin of FIG. 3 a, taken alongline 3 b-3 b;

FIG. 4 a is a perspective view of a center pin according to anotherembodiment of the present invention;

FIG. 4 b is a sectional view of the center pin of FIG. 4 a, taken alongline 4 b-4 b;

FIG. 5 is a sectional view of a center pin according to still anotherembodiment of the present invention;

FIG. 6 is a perspective view of a thermal cut-off composition, in whicha compression spring is inserted;

FIG. 7 is a sectional view showing the operation of the center pin ofFIG. 5;

FIG. 8 a is a perspective view of a center pin according to yet anotherembodiment of the present invention;

FIG. 8 b is a sectional view of the center pin of FIG. 8 a, taken alongline 8 b-8 b;

FIG. 9 a is a perspective view of a center pin according to still yetanother embodiment of the present invention; and

FIG. 9 b is a sectional view of the center pin of FIG. 9 a, taken alongline 9 b-9 b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention will now be describedwith reference to the accompanying drawings.

As shown in FIGS. 1 and 2, a lithium rechargeable battery 100 accordingto one embodiment of the present invention includes an electrodeassembly 200 having a center pin 120, a cylindrical can 300 for housingthe electrode assembly 200 and an electrolyte, and a cap assembly 400coupled to the top of the cylindrical can 300 to seal the cylindricalcan 300 and to permit electric current generated from the electrodeassembly 200 to flow toward an external device. The lithium rechargeablebattery 100 may be cylindrical in shape as shown in FIG. 1.Alternatively, the lithium rechargeable battery 100 may be prismatic inshape or may be large in size such as a battery for a HEV (hybridelectric vehicle). Additionally, the thermal cut-off compositionaccording to one embodiment of the present invention may function underhigh-temperature environments, enabling use of the battery as ahigh-capacity battery, a battery for special use (high-temperatureapplication), or a power source for a marine container box. Therefore,there is no particular limitation in the shape or type of the lithiumrechargeable battery 100.

The electrode assembly 200 comprises a cathode plate 210 having acathode current collector coated with a cathode active material layer,an anode plate 220 having an anode current collector coated with ananode active material layer, and a separator 230 positioned between thecathode plate 210 and the anode plate 220. The separator 230electrically insulates the cathode plate 210 and the anode plate 220.The electrode assembly is wound into a jelly-roll shape. The cathodeplate 210 includes a cathode current collector comprising a thin metalplate having excellent conductivity, for example aluminum (Al) foil.Although not shown in the drawings, cathode active material layers arecoated on both surfaces of the collector. The cathode plate 210 hasnon-coated portions at both ends. The non-coated portions are not coatedwith cathode active material. A cathode tab 215, generally made ofaluminum (Al), protrudes from the top of the electrode assembly 200 by apredetermined length and is joined to a non-coated portion at one end ofthe cathode plate 210.

Additionally, the anode plate 220 includes an anode current collectorcomprising a conductive thin metal plate, for example copper (Cu) ornickel (Ni) foil. Anode active material layers are coated on bothsurfaces of the collector. The anode plate 220 has non-coated portionsat both ends. The non-coated portions are not coated with anode activematerial. An anode tab 225, generally made of nickel (Ni) protrudes fromthe bottom of the electrode assembly 200 by a predetermined length andis joined to a non-coated portion at one end of the anode plate.

The electrode assembly 200 further includes insulation plates 241 and245 at the top and bottom of the assembly 200. The insulation platesprevent the electrode assembly 200 from contacting the cap assembly 400or the cylindrical can 300.

The cylindrical can 300 includes a cylindrical lateral side plate 310,which has a predetermined diameter to provide space for housing thecylindrical electrode assembly 200. The can also includes a bottom plate320 for sealing the bottom of the cylindrical lateral side plate 310.The cylindrical lateral side plate 310 is open at its top so that theelectrode assembly 200 can be inserted into the cylindrical can 300. Theanode tab 225 of the electrode assembly 200 is coupled to the center ofthe bottom plate 320 of the cylindrical can 300 so that the cylindricalcan 300 can serve as an anode. Additionally, the cylindrical can 300 maybe formed of aluminum (Al), iron (Fe) or alloys thereof. Further, thetop of the cylindrical can 300 has a crimped portion 330 that is bentinwardly to press against the top of the cap assembly 400, which iscoupled to the top opening. The cylindrical can 300 further includes achannel 340 in which a portion of the can 300 is indented inwardly topress against the bottom portion of the cap assembly 400. The channel340 is located beneath the crimped portion 330 by a distancecorresponding to the thickness of the cap assembly.

The cap assembly 400 includes a safety vent 410, a current interruptiondevice 420, a secondary protection device 480 and an upper cap plate490. The safety vent 410 is generally plate-shaped and has a protrusion410 a protruding downwardly. The safety vent 410 is disposed at thebottom of the cap assembly 400. The protrusion 410 a may deform upwardlydue to pressure generated inside the rechargeable battery. An electrodetab extending from either the cathode plate 210 or the anode plate 220is fixed to a predetermined position on the bottom surface of the safetyvent 410. For example, the electrode tab 215 extending from the cathodeplate 210 is welded to the bottom surface of the safety vent 410 toelectrically connect the safety vent 410 to the cathode plate 210. Theremaining electrode tab, for example the electrode tab extending fromthe anode plate, is electrically connected to the can 300 for example bywelding to the bottom surface 320 of the can. The safety vent 410deforms or breaks when the internal pressure of the can 300 increases,thereby breaking the current interruption device 420 and interruptingelectric current. Further, the secondary protection device 480 isdisposed on the current interruption device 420 and interrupts electriccurrent upon an over-current state. In addition, the conductive uppercap plate 490 is disposed on the secondary protection device 480 inorder to supply the cathode voltage and anode voltage to an externaldevice.

The center pin 120 is inserted into the central portion of the electrodeassembly 200. The center pin 120 has several functions. First, theelectrode assembly 200 swells during repeated charge/discharge cycles ofthe lithium ion battery, but the confines of the can prevent suchswelling from occurring near the sides of the cane. Thus, the electrodeassembly 200 swells near its center, causing deformation of theelectrode plates and short circuits. The center pin 120 prevents suchdeformation of the electrode plates. Also, when the battery reaches ahigh internal temperature due to overcharge, etc., a large amount of gasis generated in the battery. The center pin 120 serves as a path fordischarging the gas. In general, the center pin 120 is formed by windinga thin metal plate. The metal plate may be any suitable material takinginto consideration the manufacturing cost and gas discharge efficiencyof the material. The metal plate has a slit at its end. Alternatively,the center pin 120 is originally formed in the shape of a cylinderhaving no slit.

According to one embodiment of the present invention, a thermal cut-offcomposition is used as a blocker for the center pin 120. The center pin120 is coupled near the center of the electrode assembly 200, andinhibits deformation of the electrode assembly during charge/dischargecycles of the battery. Additionally, because the center pin 120 isblocked at its top and bottom ends, the void volume inside the can 300is minimized. In contrast, center pins according to the prior art areopen at the top and bottom ends, and thus the inner part of the centerpin constitutes void volume.

The thermal cut-off composition includes a material that is dissolved ordeformed at a specific temperature or under other specific conditions.Thus, the thermal cutoff composition can change the operating conditionsof a heat insulating structure. Particularly, a mixture containing atleast two organic compounds having a known melting point has improvedthermal properties and quality compared to the individual organiccompounds, as long as the compounds are mixed or combined with eachother. The product obtained from the combination of at least two organiccompounds has a melting point lower than the melting point of eitherorganic compound. The difference in the melting point between thecompounds before mixing and the product after mixing is about 5° C. ormore. In other words, the resultant thermal cut-off composition has amelting point lower than the melting point of either organic compound byat least 5° C. Such a decrease in the melting point does not depend onthe means used for combining the compounds, which can include blending,co-precipitation, co-crystallization, or the like. In addition to alower melting point, the thermal cut-off composition shows excellentchemical and thermal stability. Further, the thermal cut-off compositionis electrically non-conductive before and after melting. The blockerincluding the thermal cut-off composition is non-conductive in order toprevent an internal short circuit caused by external impact, etc. Theblocker may further include a film surrounding the center pin 120, orlids blocking the top and bottom ends of the center pin 120.

Instead of a combination of at least two organic compounds, an organiccompound having a melting point ranging from about 80 to about 150° C.may be used as the blocker for the center pin 120. In this embodiment,the range of melting points is broader than that of the combination ofat least two organic compounds. For example, as shown in the followingTable 1, 1,3-diphenylbenzene has a melting point ranging from about 84to about 88° C. Hence, it is difficult to obtain an accurate meltingpoint. However, the blocker does not need an accurate melting point, andno serious problem occurs when the melting point ranges from about 80°C. to about 150° C. In fact, such a range is important for causingdeformation of the safety vent. Therefore, an organic compoundsatisfying the aforementioned condition can be used alone as theblocker. As shown in Table 1 below, nonlimiting examples of such organiccompounds include 4-hydroxy-3-methoxybenzaldehyde, 1,3-diphenylbenzene,1,4-dibromobenzene, triphenylmethane, 4,4′-methylenebis(benzeneamine),diphenylethanedione, pentanedioic acid, n-propylhydroxybenzoate,xanthene, 3,5-dimethylpyrazole, 1,3-benzenediol,N-phenyl-2-naphthylamine, N-phenylacetamide, 9H-fluorene, m-phenylenedibenzoate, dihydro-2,5-furanedione, and the like. Nonlimiting examplesof suitable organic compounds for use in the present invention are shownin Table 1 below.

TABLE 1 Molecular CAS registration Melting point range weight CompoundNo. (° C.) (g/mol) 2H-1-benzopyrane-2-one 91-94-5 68-70 146n-butyl-4-hydroxybenzoate 94-26-8 68-69 194 Phenyl benzoate 93-99-269-72 198 Diphenyl phthalate 84-62-8 74-76 3184-hydroxy-3-methoxyxbenzaldehyde 121-33-5  81-83 152 1,3-diphenylbenzene92-06-8 84-88 230 1,4-dibromobenzene 106-37-6  87-89 235Triphenylmethane 519-73-3  92-94 244 4,4′-methylene bis(benzeneamine)101-77-9  89-91 198 Diphenylethanedione 134-81-6  94-95 210 Pentanedioicacid 110-94-1  95-98 132 n-propyl-4-hydroxybenzoate 94-13-3 95-98 180Xanthene 92-83-1 101-102 188 3,5-dimethylpyrazole 67-51-6 107-109 961,3-benzenediol 108-46-3  110-113 110 N-phenyl-2-naphthylamine 135-88-6 107-109 219 N-phenylacetamide 103-84-4  113-115 135 9H-fluorene 85-73-7114-116 166 m-phenylene dibenzoate 94-01-9 117 318Dihydro-2,5-furanedione 108-30-5  119-120 100 2,5-pyrrolidinedione123-56-8  123-125 99 3-pyridinecarboxamide 98-92-0 130-132 122 Phthalicanhydride 85-44-9 131-134 148 p-toluene sulfonamide 70-55-3 138-139 171Dimethyl terephthalate 120-61-6  140-142 194 N-(4-methylphenyl)acetamide103-89-9  149-151 149 hexanedioic acid 124-04-9  152-154 146N-phenylbenzamide 93-98-1 164-166 197 4,4′-dibromobiphenyl 92-86-4167-170 312 Mannitol 69-65-8 167-170 182 4-(1,1-dimethylethyl)benzoicacid 96-73-7 165-167 178 N-(2,6-dimethylphenyl)acetamide 2198-53-0 182-184 163 2,4-dinitrobenzeneamine 606-22-4  137-139 1837-hydroxy-4-methylcoumarine 90-33-5 190 176 5,5-diethyl-2,4,6(1H,3H,5H)-57-44-3 189-191 184 pyrimidinetrione 1,4-diphenylbenzene 92-94-4 212-213230 Inocitol 87-89-8 224-225 180 6-phenyl-1,3,5-triazine-2,4-diamine91-76-9 226-228 187 2-phenylbenzimidazole 716-79-0  293-296 1943,7-dihydro-1,3,7-trimethyl-1H-purine- 58-08-2 232-236 194 2,6-dione1,1′-bi-2-naphthol 602-09-5  214-217 286 4-hydroxy-3-methoxybenzoic acid121-34-6  209-213 168 2,3-dimethylanthraquinone 6531-35-7  210-212 2362-phenylindole 948-65-2  188-190 193 2-methylphenylacetic acid 644-36-0 88-90 150 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4- 1709-70-2 248-250 774 hydroxybenzyl)benzene Hydantoin 461-72-3  221-223 1007-hydroxycoumarine 93-35-6 230 162 Carbanilide 102-07-8  239-241 2121,5-dichloroanthraquinone 82-46-2 245-247 2771,1,1-tris(4-hydroxyphenyl)ethane 27955-94-8   245-248 3061-aminoanthraquinone 82-45-1 253-255 223 2,3,5,6-tetrabromo-p-xylene23488-38-2   254-256 422 1,5-dihydroxynaphthalene 83-56-7 259-261 1602-quinoxalinol 1196-57-2  271-272 1462,4-diamino-6-methyl-1,3,5-triazine 542-02-9  274-276 1257-chloro-4-hydroxyquinoline 86-99-7 276-279 180 Alizarine 72-48-0279-284 240 Anthraquinone 84-65-1 284-286 2082,4-diamino-6-hydroxypyrimidine 56-06-4 285-286 1262-phenylbenzimidazole 716-79-0  296 1942-amino-4-hydroxy-6-methylpyrimidine 3977-29-5  >300  1254-amino-2,6-dihydroxypyrimidine 873-83-6  >300  1272-amino-4,6-dihydroxypyrimidine 56-09-7 >300  127 Uracil 66-22-8 >300 112

In one example, 14 to 16 wt % of 7-hydroxy-4-methylcoumarine is mixedwith N-phenylacetamide in a high-speed grinding and rolling mixer for 5minutes to obtain a combination of at least two organic compounds. Afteranalyzing the resultant composition with a differential scanningcalorimeter (DSC), the composition shows a melting point of about 102°C.

In another example, 14 to 16 wt % of N-(4-methylphenyl)acetamide ismixed with 4-hydroxy-3-methoxybenzaldehyde in a high-speed grinding androlling mixer for 5 minutes. After analyzing the resultant compositionwith a differential scanning calorimeter, the composition shows amelting point of about 72° C.

As shown in FIGS. 3 b and 4 b, the center pin 110 or 120 includes a body111 or 121 with a predetermined length, which is open at its top andbottom ends. A blocker 113 or 123 containing a thermal cut-offcomposition blocks the top and bottom ends of the body, and the thermalcut-off composition melts or explodes at a specific temperature. Sincethe thermal cut-off composition may include a material capable ofdissolving in the electrolyte, the surface of the thermal cut-offcomposition can be coated with a material that is not soluble in theelectrolyte. Nonlimiting examples of suitable materials for coating thethermal cut-off composition include polyethylene (PE), polypropylene(PP) and polyimide (PI). The coating layer may be a very thin coatinglayer having a thickness sufficient to prevent the thermal cut-offcomposition from directly contacting the electrolyte.

The body 111 or 121 is strong enough to prevent deformation of theelectrode assembly 200. Nonlimiting examples of suitable materials forthe body include steel, stainless steel and aluminum. Additionally, thecenter pin 110 or 120 may be tapered 112 or 122 at its top and bottomends. When the center pin 110 or 120 is deformed by external impact, thetop and bottom ends are deformed more easily than the central portion ofthe center pin. The tapered portions 112 or 122, which have diameterssmaller than the diameter of the central portion, minimize suchdeformation.

Referring to FIGS. 3 a and 3 b, the blocker 113 may include a film thatsubstantially surrounds the body 111 including the top and bottom ends.The blocker 113 includes a material that melts or explodes at a specifictemperature. According to one embodiment of the present invention, athermal cut-off composition is used to control the melting point. Moreparticularly, the blocker 113 melts or explodes when the battery reachesan internal temperature ranging from about 80 to about 150° C., so thatthe top and bottom ends of the body 111 forming the center pin 110 areopen. As a result, the center pin 110 according to this embodiment ofthe present invention has a significantly reduced void volume due to theblockage of the top and bottom ends in the initial stage of overcharge.This permits prompt operation of the safety vent 410. However, when theinternal temperature of the battery reaches between about 80 and about150° C., there is a risk that the battery will explode or ignite. Inthis situation, the blocked center pin 110 provides minimal relief. Insuch a situation, the center pin should function as a chimney, allowingthe gas generated by the decomposition of the cyclohexyl benzene (CHB),biphenyl (BP) or the like (which is contained in the electrolyte) to beconcentrated at the safety vent 410 along the body 111 of the center pin110.

The body 111 may further include a gasifier 114 disposed inside thebody. The gasifier 111 decomposes at a predetermined voltage range togenerate gas. The gasifier 114 generally decomposes and gasifies whenthe battery is in an overcharged state, i.e. when the voltage of thebattery is about 4 to about 4.5V or greater. Nonlimiting examples ofsuitable materials for the gasifier include cyclohexyl benzene (CHB),biphenyl (BP), or the like, which are also used in the electrolyte.Cyclohexyl benzene (CHB), biphenyl (BP), or the like, contained in theelectrolyte may adversely affect the lifespan of the battery. However,because the gasifier 114 formed inside the center pin 110 does not reactwith the electrolyte in a normal state, the gasifier can include suchmaterials. In other words, if the safety vent 410 becomes deformed, thebattery becomes useless. Hence, there is no particular limitation in thematerial forming the gasifier 114, as long as the material generates alarge amount of gas.

In addition to the gasifier 114, the body 111 may further include aflame retardant 115. The flame retardant 115 is mixed with the gasifier114 and then inserted into the body along with the gasifier.Alternatively, the flame retardant 115 is packed into the body aloneunder high pressure. The flame retardant 115 significantly decreases therisk of battery ignition. Nonlimiting examples of suitable materials foruse as the flame retardant 115 include magnesium hydroxide-basedmaterials, aluminum hydroxide-based materials, phosphate-basedmaterials, and the like.

Referring to FIGS. 4 a and 4 b, the blocker 123 may include lids thatblock the top and bottom ends of the body 121. In other words, alid-shaped blocker is coupled to each of the top and bottom ends of thebody 121. Similarly, the body 121 may include a gasifier 124 and a flameretardant, as described above. When the battery reaches an internaltemperature of about 80 to about 150° C., the blocker 123 melts orexplodes and the gasifier 124 and the flame retardant 125 aretransferred to the electrolyte and the electrode assembly 200, therebyenabling prompt operation of the safety vent, interrupting theovercharged state and inhibiting battery ignition.

A center pin according to another embodiment of the present inventionwill now be described with reference to FIGS. 5, 6 and 7.

Referring to FIG. 5, the lithium rechargeable battery includes anelectrode assembly 200 having a center pin inserted in its center, a can300 for housing the electrode assembly 200, and a cap assembly forsealing the can 300. The center pin 130 may include a compressedcompression spring 137 inserted into a thermal cut-off composition 133,a body 131 surrounding the compression spring 137, and lids for blockingthe top and bottom ends of the body 131. The surface of the thermalcut-off composition 133 may be coated with a material that is notsoluble in the electrolyte. Nonlimiting examples of suitable suchmaterials include polyethylene (PE), polypropylene (PP) and polyimide(PI).

In particular, lids 138 can comprise a polymer resin strong enough thatthe lids can be opened or broken by the restoration force of thecompression spring 137. If the lids 138 are too weak, they cannot blockthe top and bottom ends of the center pin 130. If the lid 138 is toostrong, the lids 138 cannot be opened or broken, even when thecompression spring expands after the internal temperature of the batteryreaches between about 80 and about 150° C. and the thermal cut-offcomposition melts. Thus, when the lids are too strong, the safety vent410 is not deformed in due time.

The thermal cut-off composition 133 should have a melting point rangingfrom about 80 to about 150° C. The thermal cut-off composition mayinclude an organic compound, such as those described in Table 1, aloneor in combination.

Like the center pin 120, the center pin 130 may also include a gasifier134 and a flame retardant 135. The thermal cut-off composition 133 withthe compression spring 137 is inserted in the center of the center pin130. FIG. 6 is a perspective view of the thermal cut-off composition 133with the compression spring 137. The compression spring 137 is insertedinto the thermal cut-off composition 133 by insert injection molding, inwhich the compression spring 137 is introduced into a mold and thethermal cut-off composition is pushed into the mold in a molten stateusing an injector. The compression spring 137 is inserted into thethermal cut-off composition 133 in its compressed state. The modulus ofelasticity of the compression spring 137 should have an upper limitvalue in which the thermal cut-off composition 137 surrounding thecompressed compression spring is not broken. Additionally, the modulusof elasticity of the compression spring 137 should have a lower limitvalue sufficient to open or break the lids 138 when the compressionspring 137 is restored upon melting of the thermal cut-off compositiondue to an increase in the internal temperature of the battery.

FIG. 7 is a sectional view of the center pin 130 where the compressionspring 137 is restored. When the internal temperature of the batteryincreases to between about 80 and about 150° C. due to overcharge, thethermal cut-off composition 133 in the center pin 130 melts, and thecompression spring 137 can no longer be maintained in its compressedstate. Therefore, the compression spring 137 is restored and the lids138 blocking the top and bottom ends of the center pin 130, open orbreak due to the elastic energy of the compression spring. The gasifier134 and the flame retardant 135 in the center pin 130 are transferred tothe cap assembly 400, resulting in deformation or breakage of the safetyvent 410. In FIG. 7, the bold arrows indicate the discharge of thegasifier 134 and the flame retardant 135 to the exterior of the centerpin 130. Nonlimiting examples of suitable gasification members includecyclohexyl benzene (CHB), biphenyl (BP), and the like. Nonlimitingexamples of the flame retardant 135 include magnesium hydroxide-basedmaterials, aluminum hydroxide-based materials and phosphate-basedmaterials.

In another embodiment, the center pin has a structure in which both endsof the compression spring are coupled to bars, and the top and bottomends of the body are blocked with lids. In such an embodiment, when thethermal cut-off composition surrounding the compression spring melts,the compression spring is restored and the bars coupled to both ends ofthe compression spring impact the lids, thereby opening the center pin.

A center pin according to still another embodiment of the presentinvention will now be described with reference to FIGS. 8 a and 8 b.

As shown in FIGS. 8 a and 8 b, the center pin 140 according to stillanother embodiment of the present invention includes a body 141 and ablocker 143. The blocker 143 includes a thermal cut-off composition. Thecenter pin 140 may further include a gasifier 144 and a flame retardant145. The body 141 has indentations 142 near its top and bottom ends. Theindentations fix the blocker 143 in place. The indentations 142 maycomprise concave portions of the outer circumferential surface of thebody 141, and convex portions on the inner circumferential surface ofthe body. Additionally, the indentations 142 may be substantiallyring-shaped as shown in FIG. 8 a. Although not shown, the indentations142 may take any other suitable shape, such as a plurality of spots. Theindentations 142 may be formed by pressing after the top and bottom endsof the body 141 are blocked with the blocker 143. Since the blocker 143is fixed to the top and bottom ends of the body 141 by the indentations142, the center pin 140 can be sealed tightly at low temperatures. Whenthe internal temperature of the battery reaches about 80 to about 150°C., the blocker 143 melts and the center pin 140 opens. The center pin140 may further include a gasifier 144 and a flame retardant 145.

A center pin according to yet another embodiment of the presentinvention will now be described with reference to FIGS. 9 a and 9 b.

As shown in FIGS. 9 a and 9 b, the center pin 150 according to yetanother embodiment of the present invention includes a body 151 having apredetermined length and open top and bottom ends, lids 158 and sealingmembers 153 that block the top and bottom ends of the body 151.Additionally, the center pin 150 may further include a gasifier 154 anda flame retardant 155.

The top and bottom ends of the body 151 are blocked by the lids 158 andthe sealing members 153. The lids 158 may comprise a polymer resin andhave generally T-shaped cross-sections. A portion of each lid 158, hasan outer diameter smaller than the inner diameter of the body 151 toleave room for a separate sealing member 153, which is positioned wherethe lid 158 is coupled with the body 151. In other words, the sealingmembers 153 are positioned in the spaces generated between the outerdiameters of the lids 158 and the inner diameter of the body 151. Asshown in FIG. 9 b, the sealing members 153 may be positioned at the topand bottom ends of the body 151, and may be partially positioned in theinner circumferential surfaces of the upper and lower parts of the body151. In other words, the sealing members 153 may be positioned in theportions where the lids 158 contact the body 151. Although not shown,the blocker 153 may be partially formed in the inner circumferentialsurface of the upper and lower parts of the body 151.

Nonlimiting examples of suitable materials for the lids 158 includepolymer resins, such as polyethylene (PE), polypropylene (PP) andpolyimide (PI). The sealing members 153 include thermal cut-offcompositions that melt at a temperature within a specific temperaturerange. Therefore, when the internal temperature of the battery reachesbetween about 80 and about 150° C., the sealing members 153 melt and thelids 158 loosen, resulting in the opening of the top and bottom ends ofthe center pin 150.

A lithium rechargeable battery according to one embodiment of thepresent invention will now be described.

Referring to FIG. 3 b, when the battery reaches an internal temperatureof about 80 to about 150° C. or greater (e.g. 250° C.) due toovercharge, the blocker 113 (which includes the thermal cut-offcomposition) melts or explodes. Thus, the gasifier 114 is transferred tothe exterior of the center pin 110, i.e. the gasifier is transferred tothe electrolyte or electrode assembly. Upon such transfer, the gasifiergenerates a large amount of gas due to the rapid decomposition of thegasifier at a voltage of about 4 to about 4.5V or greater. The gascauses the safety vent 410 to deform or break more rapidly and allowsthe current interruption device 420 to break in order to interrupt theelectric current and prevent an increase in the internal temperature ofthe battery.

Additionally, when the internal temperature of the battery reachesbetween about 80 and about 150° C., the blocker 113 including thethermal cut-off composition melts or explodes, and the flame retardant115 is transferred to the exterior of the center pin 110. Such transferof the flame retardant 115 significantly reduces the risk of batteryignition. The above description also applies to the embodimentillustrated in FIG. 4 b.

Referring to FIGS. 5 and 7, when the internal temperature of the batteryreaches between about 80 and about 150° C., the thermal cut-offcomposition 133 surrounding the compressed compression spring 137, meltsand the compression spring elongates due to restoration force. Therestoration force causes the spring 137 to impact the lids 138, therebyopening or breaking the lids 138. The gas generated by the decompositionof the gasifier contained in the center pin 130 and the gas generatedfrom the electrolyte cause the safety vent 410 to deform or break due tothe increased internal pressure, thereby breaking the currentinterruption device 420 which then interrupts the electric current andprevent an increase in the internal temperature of the battery.

As described above, the lithium rechargeable batteries according to thepresent invention have center pins with top and bottom ends blocked bythermal cut-off compositions. Thus, the void volume inside a bare cellis reduced during initial overcharge so that the safety vent can beoperated promptly. Additionally, the thermal cut-off composition meltsat a temperature within a specific temperature range, so that thecomposition melts upon increases in the internal temperature of thebattery. This allows the center pin to serve as a gas discharge port.Upon discharge of the gas, the safety vent deforms, causing the currentinterruption device to break. Therefore, the lithium rechargeablebatteries of the present invention have improved safety.

Exemplary embodiments of the present invention have been described forillustrative purposes only. Those skilled in the art will appreciatethat various modifications, additions and substitutions to the describedand illustrate embodiments without departing from the spirit and scopeof the present invention as defined in the accompanying claims.

1. A lithium rechargeable battery comprising: an electrode assemblyhaving a center pin, wherein the center pin comprises: a compressedcompression spring positioned within a thermal cut-off composition, abody surrounding the compression spring, a top lid blocking a top end ofthe body, and a bottom lid blocking a bottom end of the body.
 2. Thelithium rechargeable battery as claimed in claim 1, wherein the thermalcut-off composition melts or explodes at a temperature ranging fromabout 50 to about 250° C.
 3. The lithium rechargeable battery as claimedin claim 2, wherein the thermal cut-off composition melts or explodes ata temperature ranging from about 80 to about 150° C.
 4. The lithiumrechargeable battery as claimed in claim 1, wherein the thermal cut-offcomposition comprises a compound selected from the group consisting of4-hydroxy-3-methoxybenzaldehyde, 1,3-diphenylbenzene,1,4-dibromobenzene, triphenylmethane, 4,4′-methylenebis(benzeneamine),diphenylethanedione, pentanedioic acid, n-propyl-4-hydroxybenzoate,xanthene, 3,5-dimethylpyrazole, 1,3-benzenediol,N-phenyl-2-naphthylamine, N-phenylacetamide, 9H-fluorene,m-phenylenedibenzoate, and dihydro-2,5-furanedione.
 5. The lithiumrechargeable battery as claimed in claim 1, wherein the thermal cut-offcomposition comprises a combination of at least two organic compounds.6. The lithium rechargeable battery as claimed in claim 5, wherein theorganic compound is selected from the group consisting of2H-1-benzopyran-2-one, n-butyl-4-hydroxybenzoate, phenylbenzoate,diphenylphthalate, 4-hydroxy-3-methoxybenzaldehyde, 1,3-diphenylbenzene,1,4-dibromobenzene, triphenylmethane, 4,4′-methylenebis(benzeneamine),diphenylethanedione, pentadioic acid, n-propyl-4-hydroxybenzoate,xanthene, 3,5-dimethylpyrazole, 1,3-benzenediol,N-phenyl-2-naphthylamine, N-phenylacetamide, 9H-fluorene,m-phenylenedibenzoate, dihydro-2,5-furanedione, 2,5-pyrollidinedione,3-pyridinecarboxamide, phthalic anhydride, p-toluene sulfonamide,dimethyl terephthalate, N-(4-methylphenyl)acetamide, hexanedioic acid,N-phenylbenzamide, 4,4′-dibromobiphenyl, mannitol,4-(1,1-dimethylethyl)benzoic acid, N-(2,6-dimethylphenyl)acetamide,2,4-dinitrobenzeneamine, 7-hydroxy-4-methylcoumarine,5,5-diethyl-2,4,6(1H,3H,5H)-pyrimidinetrione, 1,4-diphenylbenzene,inocitol, 6-phenyl-1,3,5-pyrazine-2,4-diamine,3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione, 1,1′-bi-2-naphthol,4-hydroxy-3-methoxybenzoic acid, 2,3-dimethylanthraquinone,2-phenylindole, 2-methylphenylacetic acid, 2-phenylbenzimidazole,1,3,5-methyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,hydantoin, 7-hydroxycoumarine, carbanilide, 1,5-dichloroanthraquinone,1,1,1-tris(4-hydroxyphenyl)ethane, 1-aminoanthraquinone,2,3,5,6-tetrabromo-p-xylene, 1,5-dihydroxynaphthalene, 2-quinoxalinol,2,4-diamino-6-methyl-1,3,5-triazine, 7-chloro-4-hydroxyquinoline,alizarine, anthraquinone, 2,4-diamino-6-hydroxypyrimidine,2-phenylbenzimidazole, 2-amino-4-hydroxy-6-methylpyrimidine,4-amino-2,6-dihydroxypyrimidine, 2-amino-4,6-dihydroxypyrimidine anduracil.
 7. The lithium rechargeable battery as claimed in claim 1,wherein the top and bottom lids can be opened or broken by a restorationforce of the compression spring.
 8. The lithium rechargeable battery asclaimed in claim 1, wherein each of the top and bottom lids comprise apolymer resin.
 9. The lithium rechargeable battery as claimed in claim1, wherein the body comprises a gasifier, wherein the gasifierdecomposes at a predetermined voltage range to generate gas.
 10. Thelithium rechargeable battery as claimed in claim 9, wherein the gasifiercomprises cyclohexyl benzene (CHB).
 11. The lithium rechargeable batteryas claimed in claim 1, wherein the body comprises a flame retardant. 12.The lithium rechargeable battery as claimed in claim 11, wherein theflame retardant comprises a material selected from the group consistingof magnesium hydroxide-based materials, aluminum hydroxide-basedmaterials and phosphate-based materials.
 13. The lithium rechargeablebattery as claimed in claim 1, wherein the compression spring isinserted into the thermal cut-off composition by insert injectionmolding.
 14. The lithium rechargeable battery as claimed in claim 1,wherein a surface of the thermal cut-off composition is coated with amaterial selected from the group consisting of polyethylene (PE),polypropylene (PP) and polyimide (PI).